Various techniques for recognizing a given shape contained in an image are known in the prior art.
For example, the Hough conversion is generally known as a technique for recognizing a geometric shape (such as a circle) in an image.
On the other hand, as described in Unexamined Japanese Patent Application Kokai Publication No. 2005-286940, it is known to prepare multiple face patterns in advance and conducting pattern-matching with the face appearing in an image as a technique for recognizing an object shape (such as a face) in an image.